Effects of age on closing volume during head-out water immersions

Abstract

Previous studies during head-out immersion have shown closing volume (CV) to either increase or remain unchanged. We hypothesized that these inconclusive results might be related to differences in the ages of the subjects tested. To elucidate this we studied single-breath growth argon washout tests performed by a younger group ( n=8, age 23–26) and an older group ( n=8, age 40–54) of males every 5 min during 30 min of seated, thermoneutral head-out immersion. No temporal changes in CV during immersion were observed in either group, therefore values within each group during immersion were combined. In the younger group, CV increased 77% (dry, 0.26 ± 0.11 L; wet, 0.46 ± 0.10 L; Δ = 0.20 L)( P < 0.001) but remained less than the tidal breathing range upper limit [ expiratory reserved volume + tidal volume ( ERV + V T )] . In the older group, CV increased 34% (dry, 0.83 ± 0.29 L; wet, 1.11 ± 0.19 L; Δ = 0.28 L)( P < 0.05) and was not different from ERV + V T . The absolute increase in CV during immersion did not differ between the groups. ERV decreased during immersion in both groups and was lower in the older than younger group ( P < 0.001). Alveolar plateau (phase III) slope became sleeper in the younger ( P < 0.001) but not in the older group. We conclude that during immersion: (1) The absolute increase in CV is independent of age, and (2) in subjects over 40, CV approaches the highest lung volumes reached during tidal breathing. Older subjects may be more likely to develop atelectasis during immersion and/or under other conditions in which CV is increased and tidal breathing occurs at low lung volumes.